The present invention relates to a manually operated dispensing pump for a container, such as those used to dispense liquid or pasty products, like liquid soap, hand cream or foodstuffs like ketchup and sauces. In particular, the invention provides a low cost dispensing pump, which is economical to manufacture and easy to assemble. All the pump components may be moulded from a plastics material, using conventional injection or compression moulding techniques, for example.
Conventional dispensing pumps comprise a main body, which defines a pump chamber and is held captive in the neck of a container by a collar. A piston is arranged to move telescopically within the pump chamber between a rest position and an activated position. The free end of the piston (exposed outside the pump chamber) engages with a separate spout. The piston has a central dispensing passageway, which connects with the dispensing passageway through the spout. A helical spring is provided in the pump chamber to return the piston (and hence the spout) to its rest position after dispensing. Finally, the pump comprises an inlet valve in the pump chamber and an outlet valve in the dispensing passageway in the piston. The inlet valve allows product flow from the container into the pump chamber but prevents return flow from the pump chamber into the container. The outlet valve allows product to flow from the pump chamber through the spout but prevents return flow of product or air into the pump chamber.
In the simplest conventional dispensing pumps, the inlet valve comprises a ball bearing, which engages in a seat around the inlet to the pump chamber from the container. When a partial vacuum is formed in the pump chamber, by the action of the piston, product is drawn into the pump chamber from the container, lifting the ball bearing off the valve seat. The ball bearing is retained adjacent to the valve seat by one end of the helical spring and is constrained to move within the helical windings thereof. The helical spring has a tapering cross section, to limit the extent to which the ball bearing can lift off the valve seat.
The outlet valve is provided by another ball bearing, which engages in a valve seat defined in the dispensing passageway in the piston. The ball bearing is inserted into the dispensing passageway in the piston before the spout is assembled thereto and is then retained in the piston dispensing passageway by the spout. The spout is provided with engagement means for connecting it to the piston, and is adapted to constrain the ball bearing within the piston dispensing passageway. As the product is forced out of the pump chamber, the outlet valve ball bearing lifts off its valve seat, allowing product to pass through the dispensing passageway to the spout, where it is dispensed to the user. When product is drawn into the pump chamber from the container by the partial vacuum in the pump chamber, the outlet valve ball bearing is forced back against its valve seat, preventing air or any product remaining in the spout from being drawn back into the pump chamber.
Dispensing pumps according to the prior art may also include a locking arrangement to hold the spout/piston in a fixed position and thereby prevent accidental operation of the pump. The locking mechanism may be arranged to lock the spout/piston in its activated or rest position. For example, the spout and collar may be provided with mutually co-operating screw threads, which allow the user to lock the spout in its depressed position, when the pump is not in use.
As can be appreciated from the foregoing description, even the simplest conventional dispensing pumps have a number of components, which have to be assembled prior to fitting the pump on a filled container. In the dispensing pumps known from the prior art, the helical spring is normally made of metal because of its superior compression modulus. This is required to produce a compact spring, which has sufficient inherent strength to return the piston from its activated to its rest position. The metal, helical spring is normally bought in from a third party.
During assembly of the conventional dispensing pump, the spring is free to xe2x80x9cfloatxe2x80x9d within the pump chamber. This can lead to misalignment of the spring within the pump chamber, causing unsatisfactory operation of the pump. Furthermore, as described above, in some conventional dispensing pumps, the ball bearing forming part of the outlet valve is constrained within the windings of the helical spring. In such designs, it is important that the spring traps the ball bearing but is sized such that the ball bearing can move away from the valve seat. Misalignment of the helical spring in such designs may cause unsatisfactory operation of the inlet valve and hence the pump.
The aim of the present invention is to provide a dispensing pump having few parts, which is easy to assemble, and may be entirely moulded from a plastics material. This enables the pump manufacturer to manufacture all the parts of the pump, without relying on an external source for some of the components, such as the helical spring and ball bearings for example. However, in some circumstances, metal ball bearings may be retained, because their relative abundance makes it uneconomic to mould plastic equivalents. Furthermore, metal ball bearings are easier to handle than plastic equivalents, because they are heavier and are not prone to the build up of static electricity. In particular, an aim of the present invention is to provide a plastics spring which is compact, but which still has sufficient force to return the piston/spout from its activated to its rest position.
Accordingly, the present invention provides a dispensing pump for a container, the pump comprising a housing, held fixed in relation to the container and defining a pump chamber in communication with the inside of the container; a spout, arranged to move telescopically with respect to the housing between a rest position and an activated position; a spring, arranged to return the spout from its activated position to its rest position; an inlet valve, adapted to prevent air entering the container but to allow product to enter the pump chamber from the container; and an outlet valve, adapted to prevent air entering the pump chamber but to allow product to be dispensed from the pump chamber through the spout, characterised in that the spring is made from a plastics material and has a folded configuration, having a plurality of folds.
The dispensing pump according to the invention has a plastic spring instead of the metal helical spring conventionally used in the prior art. The advantage of using a plastic spring is that it can be moulded by the manufacturer of the pump, along with the body and spout and can be adapted to provide greater functionality than the conventional metal helical spring. However, the disadvantage of making the spring from a plastics material is that plastic has a very poor compression modulus compared to metal and therefore, the spring tends to be very weak. Thus, a plastic helical spring capable of returning the spout to its rest position would have to be much larger than its metal counterpart. For this reason, it is not feasible to merely change the material from which the spring is made. In order to produce a satisfactory plastic spring, the design of the spring has to be modified to enhance the strength of its return force.
Thus, one aim of the present invention is to provide a plastics spring which will fit in a conventional size pump chamber but which has sufficient inherent force to return the spout/piston to its rest position. The inventors have found that a spring having a folded configuration with a plurality of folds has sufficient inherent resilience for this task. This spring configuration can be easily moulded using conventional techniques and is compact enough to fit in a pump chamber of conventional size.
An advantage of this configuration is that radial deflection of the spring under compression is minimised, thereby ensuring that the spring does not bind against the side-walls of the pump chamber as it is compressed. Another advantage of the folded plastic spring configuration is that it has end plates at each end of the spring. These end plates may be adapted to provide the spring with greater functionality. For example, the end plates may be adapted to constrain the inlet valve, outlet valve or both within their respective housings. The end plate may even be adapted to provide a valve seat in which a valve member can rest to prevent flow through the valve in one direction.
Where the valve comprises a valve member, arranged to seat against a surface provided in the housing, the housing may be adapted to define a valve chamber within which the valve member is constrained to move. The end plate of the spring may then be used to define the end wall of the valve chamber. The valve member is allowed to float freely within the confines of the valve chamber, which can be designed for efficient operation of the valve. In some prior art designs, where a valve member is constrained to move within the confines of the windings of the helical spring, the valve member may operate less efficiently, causing unsatisfactory operation of the pump. If the valve member is allowed too much travel away from the valve seat, the valve will be difficult or impossible to prime. If the valve member is allowed insufficient travel, the valve may jam or fail to pump. Provision of a separate valve chamber allows the movement of the valve member to be more closely controlled. this arrangement allows the designer the freedom to provide a valve member that is not spherical. One end of the valve chamber preferably has an opening, which is sized to allow the valve member to be easily inserted into the chamber. The spring is inserted into the pump chamber and its end plate is arranged to close the opening in the valve chamber, holding the valve member captive therein.
Preferably, the body of the pump defines the valve chamber and the spout is adapted to provide a piston, which can move telescopically within the valve chamber. In the pump according to the invention, the piston and spout are formed integrally with one another. A tubular seal may be provided inside the piston portion of the spout. The seal may be adapted to define the valve seat for the outlet valve. Alternatively, the valve seat may be defined in the end plate of the plastic spring. The tubular seal is designed to extend below the free edge of the piston and flares radially outwardly to provide a seal against the side wall of the pump chamber. Preferably, the tubular seal is made from a more flexible material than the pump chamber. This ensures that the flared skirt of the tubular seal, extending beyond the free edge of the piston, is able to conform to the surface of the pump chamber and form a good fluid seal therewith, even when the piston moves telescopically within the pump chamber.
The piston/spout may be provided with a locking arrangement, which locks the piston relative to the housing, thereby preventing accidental operation of the dispensing pump. According to the invention, the locking arrangement is arranged to lock the piston in its rest position, with the spring substantially unstressed. This reduces the effects of creep in the plastic spring. When a plastic component is left for a prolonged period under load, the plastic material tends to undergo permanent deformation or creep, which would effect the behaviour of the plastic spring and hence its performance.
The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: